Refund claim - Once the input credit is legally taken and utilized on the dutiable final product, it need not be reversed on the final product being exempted subsequently. Only if any products are purchased subsequent to the said exemption and if any tax is paid on such inputs, as the final product is exempted from payment of tax, the assessee would not be entitled to avail the Cenvat credit on such inputs - No reversal can be claimed before amendment to Rules - credit reversed wrongly to be allowed as refund - Tri